Modding still exists, only it's much smaller now, due to many issues: -Current tools released by Dev's are a joke in many cases, with requirements for the community to bring the rest, and sometimes, will send you a D&C letter if you do due to certain restrictions. -Many of the tools/assets used in the final games most…
Also some new games' SDKs/modding tools are a bit of a crippled joke these days. Serious Sam 3 BFE is a nice example of such a game. It won't even let you export their stock skeletons for rigging and reference. WTF Also not all Valve games are proper for modding. Left4Dead 2 for example, has a BROKEN addons menu, broken…
Mods don't have to include environments. They could be purely code as an example. No giant amount of data to distribute there. Like what? Most of the modded titles around now are 5 years old, or even older. With what remains it's largely Source that retains a sizeable community (though Crysis is still dragging its feet).…